a futile endeavor, a brave but useless attempt

(formal, dated) motorcycle

set free / release / fire / shoot / emit / banish / liberate

to stand guard, to look out (for a suspect or enemy)

challenge / contend for / make love to

tide / saltwater / opportunity

to look at; to gaze

swell, dilate, distend, bulge

tune, tone, meter, key (music) / writing style / to prepare, to exorcise / to investigate / to harmonize, to mediate

stick; apply; paste