( Day ( ( ( The measurement ) ( of ( a day ) ) ) ( ( is ( ( the time ) ( it ( takes ( a ( planet ( to ( ( rotate once ) ( on ( its axis ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (NNP Day)) (NP (NP (DT The) (NN measurement)) (PP (IN of) (NP (DT a) (NN day)))) (VP (VBZ is) (NP (NP (DT the) (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (NP (DT a) (NN planet) (S (VP (TO to) (VP (VB rotate) (ADVP (RB once)) (PP (IN on) (NP (PRP$ its) (NNS axis)))))))))))) (. .)))
Day The measurement of a day is the time it takes a planet to rotate once on its axis.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))