Meaning : wasteful or immoral behavior
Example : Letting the lights on when nobody’s in the room is a profligacy action.
Meaning : having or showing no skill
Example : The way she guided us yesterday proves that she is inept in handling a trip.
Meaning : express regret towards something
Example : The lyric in his new song shows lament and sorrow.
Meaning : thin, not thick
Example : My country has areas with sparse population
Meaning : workable
Example : the proposed investment was economically viable.