Teach yourself these words! It will build your vocabulary. These are all from Merriam-Webster Dictionary

Some of the Most frequently Used Words in English

in·ves·ti·ga·tor
NOUN
a person who carries out a formal inquiry or investigation:
"accident investigators are at the crash site

Oxford Dictionary

investment
NOUN
the action or process of investing money for profit or material result:
"a debate over private investment in road-building" · [more]
synonyms:
investing · speculation · expenditure · outlay · funding

man·ner
NOUN
a way in which a thing is done or happens:
"taking notes in an unobtrusive manner"
synonyms:
way · fashion · mode · means · method · system · style · approach · [more]
a style in literature or art:
"a dramat

mas·sive
ADJECTIVE
massive (adjective)
large and heavy or solid:
"a massive rampart of stone"
synonyms:
huge · enormous · gigantic · very big · very large · great · giant · colossal · mammoth · vast · immense · tremendou