shadowing

(noun) the act of following someone secretly. Synonyms: tailing.

(verb) follow, usually without the person's knowledge. Synonyms: shadow. Example: "The police are shadowing her."

(verb) cast a shadow over. Synonyms: shadow, shade, shade off.

(verb) make appear small by comparison. Synonyms: shadow, overshadow, dwarf. Example: "This year's debt dwarfs that of last year."