凹む

Etymology 1
Verb derived from noun /  + verbalizing suffix, with suffix  mutating to  due to the preceding syllable.

Verb

 * 1) to become hollow, cave in, sink in

Usage notes
The transitive form is /. Consequently, the potential form is the same as the passive form,, instead of as shown in the table above.

The spelling is used more often for, because the alternative spelling  can also be read as  (see below).

Etymology 2
→

Contraction of, itself a compound of.

Verb

 * 1) to become hollow, cave in, sink in: see the kubomu reading above
 * 2) to decline below a certain point, to become less
 * 3) to be stuck to be at a loss: see.
 * 4) to yield, to submit
 * 5)  to be bummed out