trough (n.)
- adit
- aerospace
- airspace
- alveolus
- amplitude
- antinode
- antrum
- aqueduct
- armpit
- basin
- billow
- bore
- bottom
- bottoms
- bowl
- breakers
- bump
- burrow
- canal
- canalization
- cavity
- ceiling
- chamfer
- channel
- chisel
- chop
- choppiness
- chute
- comb
- comber
- concavity
- conduit
- course
- crack
- crater
- crest
- crimp
- crosswind
- crypt
- cup
- cut
- dado
- dale
- dell
- depression
- diffraction
- dig
- dike
- dingle
- dip
- ditch
- dredge
- drill
- drive
- duct
- eagre
- egress
- entrance
- entrenchment
- exit
- flute
- fog
- fold
- follicle
- fosse
- frequency
- front
- furrow
- gap
- gash
- gill
- glen
- goffer
- gouge
- groove
- grove
- grub
- guide
- gully
- gutter
- ha-ha
- heave
- hole
- hollow
- ingress
- interference
- ionosphere
- kennel
- lacuna
- lift
- light
- lop
- lower
- mine
- moat
- node
- overcast
- pass
- passage
- passageway
- peak
- penstock
- period
- pit
- pleat
- plow
- quarry
- rabbet
- ravine
- ray
- reinforcement
- resonance
- riffle
- rifle
- ripple
- rise
- roll
- roller
- roughness
- rut
- sap
- scoop
- score
- scrabble
- scrape
- scratch
- sea
- send
- shell
- shoot
- shovel
- sink
- sinus
- slit
- socket
- soup
- space
- spade
- stratosphere
- streak
- striate
- surf
- surge
- swell
- trench
- tropopause
- troposphere
- tsunami
- tunnel
- turbulence
- undulation
- vale
- valley
- visibility
- wadi
- wave
- wavelength
- wavelet
- way
- wrinkle
