Capable of being added; suitable or possible to combine through addition with other things.
From 'add' (Latin addere, to put to) plus the suffix '-able' (from Old French, capable of); standard English formation for describing what can be done to a thing.
In programming and databases, checking if something is 'addable' is fundamental—you need to know before you try combining values whether they'll work together without breaking everything.
Complete word intelligence in one call. Free tier — 50 lookups/day.