is there a difference between さみしい and さびしい？

Question

Both mean "lonely" and appear to be valid readings for 寂しい.

Is there a difference in nuance? Is this difference due to dialect?

Answer 1

According to an answer to a similar question on Goo's oshiete site:

「さびしい」 is generally used in two ways (roughly equivalent to how the english "lonely" is used):

1. an emotional state of emptiness, isolation, or a feeling of lacking
   • Examples: 「さびしい正月を迎える」「ふところがさびしい」
2. quiet and empty of people or sounds
   • Example: 「さびしい山道」

These two meanings are essentially subjective and objective, respectively, and さびしい can be used in either. さみしい, however, generally tends much more toward the subjective/emotional meaning of (1).

As for whether it is dialectal, I do not believe that it is. The answer to the question linked above suggests that this b→m sound change is not limited to さびしい／さみしい alone, and cites other examples such as 煙る（けむる／けぶる）and [目を]つぶる／つむる.

Update: Inspired by @Axioplase's comment below, I investigated the b/m sound change, specifically regarding 「寒い」.

Wiktionary suggests that in fact, the origin of さむい is the same as さびしい: さぶし. At some point this split into さびし (which later became さびしい and subsequently さみしい), while さぶし also went on to form さぶい -- and subsequently, the modern さむい which we use today.

Unfortunately, I can't find many other (reputable) sources for the etymology of さむい.