I found it interesting too, but check out the first definition in the dictionary:
さびし・い 3 【寂しい/▼淋しい】
(形)[文]シク さび・し
〔「さぶし」の転。中古以降の語〕
(1)あるはずのもの、あってほしいものが欠けていて、あ 桙スされない気持ちだ。物足りない。さみしい。
「彼の顔が見えないのは―・い」「タバコをやめると口 が―・い」「ふところが―・い」
Particularly have a look at the second and third example sentences. I suppose this goes to a few points:
1) Just because you have a gloss for a word in English doesn't mean you have the whole meaning of the word.
2) Just because you feel like you've come to know a word fairly well doesn't mean you actually know it.
I had a similar experience with 断る. Check that one out (it doesn't just mean "refuse," "decline," etc.):
ことわ・る 3 【断る(断わる)】
(動ラ五[四])
〔「こと(事・言)割る」の意〕
(2)前もって事情を伝えて、了解を求める。承認・承諾あ ≠゚る。
「事前に―・らずに会議を欠席する」「―・っておくが 、これは私個人の意見である」