Hello! It's me again with some questions.

Browsing through the dictionaries at http://www.teanglann.ie/, I've come across several words that mean 'twilight' or 'fading light'. Namely, breacsholas, clapsholas, geamhsholas, lagsholas, leamhsholas, and meathsholas.

Can someone please tell me about their etymology and usage?

breac- = speckled, dappled
clap = ?
geamh- = winter
lag = weak
leamh = soft, weak
meath- = failing, fading, weak

GRMA, a Labhráis!

Are they all interchangeable or does their usage depend on the context and/or dialect?