kilogram - mass, second - ?

TIME
List of words for the clue kilogram - mass, second - ? from the crossword:
UNIT POUND LITER TONNES KILO YARD MILE METRE METER LITRE KILOMETRE KILOCALORIE KG INCH HECTARE GALLON DISTANCE CENTEMETRE CALORIE
WordClue
ACREkilogram - pound, hectare - ?
INCHkilogram - pound, centemetre - ?
MASSsecond - time, kilogram - ?
MILEkilogram - pound, kilometre - ?
UNITkilogram or hertz
YARDkilogram - pound, metre - ?
GROUPcrowd, mass
HORDEbattalion, mass
LITREpound - kilogram, gallon - ?
METERmass - kilogram, distance - ?
METREpound - kilogram, yard - ?
OUNCEunit of mass
POUNDmetre - yard, kilogram - ?
GALLONkilogram - pound, litre - ?
SECONDmass - kilogram, time - ?
HECTAREpound - kilogram, acre - ?
DISTANCEkilogram - mass, meter - ?
KILOGRAMtime - second, mass - ?
KILOMETREpound - kilogram, mile - ?
CENTEMETREpound - kilogram, inch - ?
DISTANCEkilogram - mass, meter - ?
UNITkilogram or gallon