This declension was declining in use, with a number of masculine and feminine nouns moving to the second declension. Masculine and feminine fourth declension nouns Basic paradigm manus, manus . The -ubus endings in the dative, ablative and locative plurals are used for acus , arcus , quercus , tribus , and usually for lacus and portus . The -ibus ending is used for most other fourth declension nouns.
Some examples acus, -us . nf.
Borrowed words of dubious origin and usage When Latin borrows nouns, say from Greek, or perhaps through a time warp from English, these nouns may have somewhat creative declensions. These are are all verbal nouns called supines . Generally in Latin, the supine is restricted to accusative and ablative fourth declension forms. A few supines exist in other cases as well. In the nominative, these take the form of the perfect passive participle, but they are present active in meaning.