What is an introductary word?

Question

thank you

Answer 1

Words at the beginnings of sentences or clauses, such as these -

because
if
when
though
although
when
after
moreover
therefore

... and many others.

Answer 2

Some are called subordinating conjunctions:
http://grammar.ccc.commnet.edu/grammar/conjunctions.htm#subordinating_conjunctions

Others are conjunctive adverbs:
http://grammar.ccc.commnet.edu/grammar/transitions.htm#transitions

Answer 3

Thank you

Answer 4

You're very welcome.