The following are described as "imitative" in the etymology section of their entries:
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> Found: 371 entries
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> 
>   1. ajutment
>   2. altry
>   3. anatical
>   4. applease
>   5. arbiter
>   6. ascent
>   7. baff
>   8. baff
>   9. baugh; baw
>  10. baw-waw
>  11. bebop
>  12. beep
>  13. beep
>  14. bewh
>  15. biff
>  16. bish
>  17. blaff
>  18. blah
>  19. blare
>  20. blat
>  21. blat
>  22. blea
>  23. bleat
>  24. blodge
>  25. bom
>  26. bong
>  27. boobook
>  28. boom
>  29. bourdon; burdoun
>  30. bow-wow
>  31. brrr
>  32. bruzz
>  33. bubble
>  34. buln-buln
>  35. bum
>  36. burble
>  37. burp
>  38. burr
>  39. cank
>  40. caterwaul
>  41. caw
>  42. cawk
>  43. chaack
>  44. chack
>  45. chack-chack
>  46. cheep
>  47. cheer
>  48. chick
>  49. chicker
>  50. chipper
>  51. chirl
>  52. chirp
>  53. chit
>  54. chit-chit-chat
>  55. chock
>  56. chuck-will's-widow
>  57. chunter
>  58. clack-clack
>  59. clippety-clop
>  60. cloop
>  61. clop
>  62. cluck
>  63. cluck
>  64. clucker
>  65. cocket
>  66. coo
>  67. crawk
>  68. crool
>  69. croup
>  70. crout
>  71. cuckoo
>  72. curkle
>  73. dah
>  74. decerniture
>  75. dickcissel
>  76. didgeridoo
>  77. diederik; diedrik
>  78. dink
>  79. dit; di
>  80. doo-wop
>  81. flibbertigibbet
>  82. flish
>  83. flush
>  84. fuzz
>  85. gag
>  86. garre
>  87. giggle
>  88. gladish
>  89. go-away
>  90. gobble
>  91. golf
>  92. grump
>  93. hackee
>  94. harrumph
>  95. hoop
>  96. huff
>  97. jingle
>  98. jirble
>  99. kaak
> 100. kae
>   1. keak
>   2. keelie
>   3. kewt
>   4. kill-cu
>   5. killdee; killdeer
>   6. knab
>   7. logger
>   8. lull
>   9. lulliloo
>  10. lumber
>  11. mammer
>  12. maunder
>  13. miff
>  14. mim
>  15. mock
>  16. mop
>  17. mopoke; morepork
>  18. nattle
>  19. neeze
>  20. neigh
>  21. neigher
>  22. nicher
>  23. nicker
>  24. nickety-nock
>  25. niddle
>  26. niminy-piminy
>  27. nipper
>  28. nuzzing
>  29. oompah; oom-pah
>  30. oomph
>  31. paver
>  32. pech
>  33. pheal
>  34. phoebe
>  35. pime
>  36. pipit
>  37. plasmatic
>  38. qua-bird
>  39. quack
>  40. quack
>  41. quack
>  42. quackle
>  43. quack-quack
>  44. quail
>  45. quake
>  46. qualm
>  47. quap
>  48. quark
>  49. quawk
>  50. quawk
>  51. queck
>  52. quink
>  53. quirk
>  54. quit
>  55. ramp
>  56. rasp
>  57. rickle
>  58. ricky-tick
>  59. rigadig
>  60. ring
>  61. rinky-tink
>  62. rippit
>  63. roar
>  64. roocoocoo
>  65. rook
>  66. rope
>  67. rottle
>  68. rounce robble hobble
>  69. rouncing
>  70. roup
>  71. rout
>  72. rub-a-dub
>  73. ruff
>  74. ruff-raff
>  75. rustle
>  76. ruttle
>  77. scat
>  78. screel
>  79. shaffle
>  80. shoy-hoy; shoyhoy
>  81. simper
>  82. sing-sing
>  83. siss
>  84. sistle
>  85. sizz
>  86. sizzle
>  87. skelloch
>  88. skelp
>  89. slap
>  90. slap
>  91. slat
>  92. slatter
>  93. slodge
>  94. sloff
>  95. slosh
>  96. slosh
>  97. sluffer
>  98. slump
>  99. slumper
> 100. slush
>   1. slush
>   2. smack
>   3. small
>   4. smash
>   5. snaffle
>   6. snar
>   7. snark
>   8. snash
>   9. snatter
>  10. snavel
>  11. sneck
>  12. sneer
>  13. snick
>  14. snicker
>  15. snick-up
>  16. sniff
>  17. sniffle
>  18. snift
>  19. snifter
>  20. snigger
>  21. sniggle
>  22. snip-snap
>  23. snirt
>  24. snoach
>  25. snob
>  26. snock
>  27. snop
>  28. snop
>  29. snore
>  30. snort
>  31. snuff
>  32. snur
>  33. snurt
>  34. snush
>  35. snuttering
>  36. sob
>  37. sock
>  38. sosh
>  39. soss
>  40. soss
>  41. souse
>  42. south-southerly
>  43. spang
>  44. spank
>  45. spat
>  46. spat
>  47. spink
>  48. spit
>  49. splatch
>  50. splatter
>  51. splodge
>  52. sploshy
>  53. splotch
>  54. splunge
>  55. splurge
>  56. splurge
>  57. splurt
>  58. splutter
>  59. sposh
>  60. spraich
>  61. sprinkle
>  62. spuffle
>  63. sputter
>  64. squab
>  65. squabble
>  66. squail
>  67. squall
>  68. squark
>  69. squark
>  70. squash
>  71. squatter
>  72. squawk
>  73. squeak
>  74. squeal
>  75. squeck
>  76. squelch
>  77. squib
>  78. squidge
>  79. squidge
>  80. squiggle
>  81. squiggle
>  82. squirk
>  83. squirm
>  84. squish
>  85. squish-squash
>  86. squit
>  87. squitter
>  88. squizzle
>  89. squodgy
>  90. sqush
>  91. suffet
>  92. suther
>  93. swash
>  94. swish
>  95. swish
>  96. switter
>  97. swoosh
>  98. tu-whit; tu-whoo
>  99. twiddle
> 100. twig
>   1. twingle
>   2. twirl
>   3. twite
>   4. twitter
>   5. twizzle
>   6. ugh
>   7. uh
>   8. uh-huh
>   9. uh-uh
>  10. ullagone
>  11. ululate
>  12. ululu
>  13. um
>  14. umph
>  15. veery
>  16. vim
>  17. wharl
>  18. whaup
>  19. wheak
>  20. wheep
>  21. wheeple
>  22. wheetle
>  23. whick
>  24. whicker
>  25. whing
>  26. whinny
>  27. whip-tom-kelly
>  28. whish
>  29. whish
>  30. whist
>  31. whist
>  32. whit
>  33. whitter
>  34. whoosh
>  35. whrinny
>  36. whuff
>  37. whurl
>  38. whush
>  39. whute
>  40. whutter
>  41. wimick; wimmick
>  42. wishtonwish
>  43. wistiti
>  44. wlaffe
>  45. wlite
>  46. woomph
>  47. wough
>  48. woul
>  49. wow
>  50. wow
>  51. wowl
>  52. wow-wow
>  53. wow-wow
>  54. wrag
>  55. wratling
>  56. wraw
>  57. wrawl
>  58. wrele
>  59. wrig
>  60. wrough
>  61. yar; yarr
>  62. yarwhelp
>  63. yatter
>  64. yech
>  65. yeep
>  66. yex; yesk
>  67. yoll
>  68. yow
>  69. yuck
>  70. yuck
>  71. zip