ETYM Pref. in- not + adequate: cf. French inadéquat.
1. Not sufficient to meet a need; SYN. poor, short.
2. (Sometimes followed by 'to') Not meeting the requirements especially of a task.

ETYM Latin insufficiens, -entis. Related to In- not, and Sufficient.
Of a quantity not able to fulfill a need or requirement; SYN. deficient.