Most are masculine. There are around 20-30 important nouns of the fourth declension: these are given following the declension..

                                SINGULAR                         PLURAL

NOMINATIVE           senatUS                             senatUS

GENITIVE                 senatUS                             senatUUM

DATIVE                     senatUI                              senatIBUS

ACCUSATIVE           senatUM                             senatUS

ABLATIVE                 senatU                               senatIBUS

Note- The genitive singular, nominative plural and accusative plural all have a long u in the ending.

Common fourth declension nouns

senatus - senate            exercitus - army            fructus - fruit

manus - hand                versus - line of verse    metus - fear

casus - accident, chance  domus - house          usus - experience

impetus - attack              sumptus - expense     sensus - feeling

spiritus - breath               genu - knee                cornu - horn

manus is feminine.

Again, we are dealing with a few words: the major examples follow the declension. The gender for most fifth declension nouns is feminine.

                                SINGULAR             PLURAL

NOMINATIVE             rES                         rES

GENITIVE                   rEI                          rERUM

DATIVE                      rEI                          rEBUS

ACCUSATIVE            rEM                        rES

ABLATIVE                 rE                           rEBUS

Common fifth declension nouns

res - thing                    spes - hope                dies - hope

facies - face, appearance   scabies - mange    fides - loyalty

dies is masculine.