( ( ( ( ( ( half life ) ( a unit ) ) ( of ( ( relative time ) ( measuring ( ( ( ( ( ( the rate ) ( ( at which ) ( ( a ( radioactive substance ) ) decays ) ) ) , ) or ) ( -LRB- ( ( more generally ) -RRB- ) ) ) ( the rate ) ) ) ) ) ) ( of decrease ) ) ( for ( ( any process ) ( that ( decreases exponentially ) ) ) ) ) . )
(ROOT (NP (NP (NP (NP (DT half) (NN life)) (NP (DT a) (NN unit))) (PP (IN of) (NP (NP (JJ relative) (NN time)) (VP (VBG measuring) (NP (NP (NP (DT the) (NN rate)) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (DT a) (JJ radioactive) (NN substance)) (VP (VBZ decays))))) (, ,) (CC or) (PRN (-LRB- -LRB-) (FRAG (ADVP (RBR more)) (ADVP (RB generally))) (-RRB- -RRB-)) (NP (DT the) (NN rate))))))) (PP (IN of) (NP (NN decrease))) (PP (IN for) (NP (NP (DT any) (NN process)) (SBAR (WHNP (WDT that)) (S (VP (VBZ decreases) (ADVP (RB exponentially))))))) (. .)))
half life a unit of relative time measuring the rate at which a radioactive substance decays, or (more generally) the rate of decrease for any process that decreases exponentially.
(ROOT (S (NP (DT The) (NN decay) (NN rate)) (VP (VBZ is) (VP (VBN measured) (PP (IN in) (NP (NP (DT a) (NN unit)) (VP (VBN called) (NP (DT the) (NN half-life))))))) (. .)))