(Tsume ni hi wo tomosu; “To light one’s (finger)nail”)
Extreme penny-pinching. To be incredibly poor, or just incredibly stingy with one’s money. Being unable to afford even a candle – or unwilling to buy one – and instead making light at night by setting flame to one’s own nails.
This is grammatically a complete sentence, although you’ll usually see it as a clause or phrase in a longer sentence. The verb is 点す (alternately 灯す), (tomosu), “to light (a fire).” The particle を (wo) marks as direct object of this verb the preceding noun 火 (hi, rhyming with English pronoun “he”), “fire.” Finally we have the particle に (ni) in its function as a location-marker, acting on the noun 爪 (tsume), “finger/toe nail.”
It’s not uncommon to render tomosu in kana as ともす, and 灯す is a second valid kanji to use, but replacing tomosu with 燃やす (moyasu, “to burn”) is an error.
This is the つ entry for the Osaka iroha karuta set. One of my sources also ties it to Kefukigusa, an early Edo-period collection of haiku compiled by Matsue Shigeyori.
(“Daigakusei to daigakuinsei no toki wa, tsume ni hi wo tomosu hodo mazushii kurashi wo shite kita no de, gaishoku de sura nan to mo zeitaku na kimochi desu yo.”)
[“As an undergrad and grad student, I was poor enough to burn my nails for light, so simply eating at a restaurant feels ”]