All 4 Uses

lament
in
Killing Lincoln
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"The nervousness," a Confederate major will remember, "resulting from this constant strain of starvation, fatigue and lack of sleep was a dangerous thing, sometimes producing lamentable results."†
p. 33.2

lamentable = regrettable

standard suffix: The suffix "-able" means able to be. This is the same pattern you see in words like breakable, understandable, and comfortable.
"My shoes are gone," a veteran soldier laments during the march.†
p. 47.1 *

laments = expresses grief or regret
They are now in church or at home repenting, leaving the local merchants to lament the momentary loss of the booming business they've enjoyed the past few days.†
p. 163.3

lament = express grief or regret
"I have given my husband to die," she laments, wishing that it could have been her instead.†
p. 231.5

laments = expresses grief or regret

Definitions:

(1) (lament)
to express grief or regret
(2) (meaning too rare to warrant focus)
Although lament typically refers to a feeling or simple vocal expression, it can refer to a vocal expression as complex as a sad song or poem. It can even refer to sad, but non-vocal music -- as when Tennessee Williams references background music in A Streetcar Named Desire.