雨さえなければ - meaning


What kind of word is 雨さえ and how does it work with なければ since it does not seem
to be a adjective or verb?

full sentence:

> 雨さえなければ、七月四日に花火大会を行うつもりです。 (As long as it doesn't rain, we intend to hold
> the fireworks display on July 4th.)




According to Martin, さえ has three meanings, the basic meaning being 'in
addition', e.g. なるほど風が大分強くなって雨さえ降りだしたようである, 'it seems that the wind became
really quite strong, and in addition it started to rain'. More frequently it
means 'even', much like も which can in fact be attached to さえ、さえも. The third
meaning, here, is to narrow the focus onto some element (adjunct of the verb,
or the verb itself) before a verb + えば (provisional), conveying the meaning of
'(if) just', e.g. 暇さえあれば, 'if there just be time', 薬さえ飲めば, 'if you just take
your medicine', with emphasis on 'medicine', while 薬を飲みさえすれば puts the emphasis
on the 'taking'; we would distinguish this with stress in English.

