Per Random House Webster's College Dictionary, Ed. 1991,
available
suitable or ready for use; of use or service; at hand:
I used whatever tools were available.readily obtainable; accessible:
available resources.
valid
sound; just; well-founded: a valid reason.
producing the desired result; effective:
a valid antidote for gloom.having force, weight, or cogency; authoritative.
legally sound, effective, or binding; having legal force:
a valid contract.
Per Collins-Robert English-French Ditionary, Ed. 1985,
availability
n
(a) [material, people] disponibilité f
(b) (US: validity) validité f
available
adj
(a) personnel disponible; thing disponible, utilisable
(b) (US: valid) valable, valide (for pour)
My question is, what's the difference between "available" and "valid" in the sense "having sufficient power or efficacy"?
In addition, absent clear context, "can't the word "available" sound sort of ambiguous as to whether it's "obtainable/accessible" or "having sufficient power or efficacy" that actually is meant?
Please, consider the following example:
The period for which these tickets are available is 3 months
The period of availability for these tickets is 3 months
could be understood as meaning,
The period for which these tickets are obtainable/accessible is 3 months
But also,
The period for which these tickets are valid (=effective) is 3 months
Best Answer
Look in Merriam-Webster, definition 2.
Similarly, the OED says:
It's a specialized usage, and cannot be used for concert or train tickets. The OED also gives a (probably obsolete) U.S. political sense of available; it seems that a candidate was available if he had a good chance of winning. However, this really isn't a synonym of valid.
ADDED:
The word available can mean valid for train tickets in the U.K. and other countries, but I have never seen this usage in the U.S. See the comments.