Compound of相合(aiai,“doing things together”) +傘(kasa,“umbrella”). Thekasa changes togasa as an instance ofrendaku (連濁).
相合傘 has a strong romantic implication, stemming in part from a play on words. The first two characters are pronouncedあい(ai), the same as the word愛(ai,“love”), and thus the connotation is that both people under the umbrella are in love.
asimplisticdoodle of anumbrella, usually topped with aheart, with the names of two people who are said to be in love written on either side of itshandle (compare the writing of names inside a heart)