As well, there's some good advice on the use of hyphens in compound adjectives at http://www.grammar-monster.com/lessons/ ... ctives.htm
Note the advice on the usefulness of the hyphen when the meaning may change. I think that's an important insight.
I suspect there aren't that many nouns (such as leg, head, eye) that, when used as part of compound adjectives, acquire what looks like a past tense form (legged, headed, eyed). I wonder if they are all related to body parts (hand, finger, etc.)?
Many other nouns exhibit another behaviour when used as adjectives:
a one-minute walk / a twenty-minute walk (a walk of twenty minutes)
a two-day outing (an outing that lasts two days)
a two-tone car (a car painted in two tones)
a triple digit increase in value (a value that increases by three digits)
The notable thing here is the use of the singular. That's to be expected, right? Adjectives in English have no number. Are there any exceptions? I don't think so.