puella

Puella, puellae, f. First declension, and the noun every beginner declines first, largely because it is so regular that nothing distracts from the endings.

Formally it is a diminutive of an older puera, the feminine of puer, so the literal sense is "little girl". The diminutive force wore off early, and puella covers anything from a child to a woman of marriageable age. The love poets made it their standard word for the beloved: Catullus writes puella and expects no further description. Note that it says nothing about status. A slave girl is a puella, and so is a young wife, so translating it as "maiden" imports a delicacy the Latin does not have. Watch the genitive singular and nominative plural, both puellae.