Lovebird and Sweetheart

Lovebird noun - Small Australian parakeet usually light green with black and yellow markings in the wild but bred in many colors.

Sweetheart and lovebird are semantically related In some cases you can replace term "Sweetheart" with "Lovebird", this nouns are similar.

Sweetheart noun - A person with whom one is in love.

Lovebird and sweetheart are semantically related in person whom another loves topic. Sometimes you can use "Lovebird" instead a noun "Sweetheart".