alternate word forms in meta keyword tags

Should you include alternate forms (including plurals) in your keywords, or would that be considered spam? In particular I have phrases that can be separated by spaces or dashes (should i use both forms?) and words that are plural and singular? i know meta keyword tags are devalued on some engines and i'm not trying to keyword stuff... just want to make sure if i should be including the alternate forms that i'm not missing out on clicks because of it.