'tillability' originates from Modern English formation, specifically from the adjective 'tillable' combined with the noun-forming suffix '-ity' (via the productive '-ability'), where 'till' ultimately derives from Old English 'tilian' meaning 'to cultivate'.

'tillability' developed from Middle/Modern English derivational processes: Old English 'tilian' (to cultivate) produced the verb 'till' in Middle English; that verb formed the adjective 'tillable' ('till' + '-able'), and in Modern English the noun-forming suffix '-ity'/'-ability' yielded 'tillability' as a technical noun.

Initially the root referred simply to the action 'to cultivate'; over time the derived compound came to denote the property or suitability of land for cultivation — the current meaning 'suitability for tilling'.