too

Meanings

1. 1
   adv

   in addition

   They are envious, too.

2. 2
   adv

   Likewise.

   The preposterous altruism too![…]Resist not evil. It is an insane immolation of self—as bad intrinsically as fakirs stabbing themselves or anchorites warping their spines in caves scarcely large enough for a fair-sized dog.

3. 3
   adv

   Also, in addition marks a statement as equally valid as the preceding one.

   There has been a cutback in federal subsidies. Rates have been increasing too.

4. 4
   adv

   To an excessive degree, more than enough indicates that the degree of a quality is more than what is needed or wanted.

   Near-synonyms: extremely, unnecessarily, all too

5. 5
   adv

   To a high degree, very.

   She doesn't talk too much.  I'm not too sure about this.

6. 6
   adv

   Used to contradict a negative assertion with present and simple past forms of be, do, and auxiliary verbs

   You're not old enough yet. ― I am too!

7. 7
   adv

   Used for emphasis, without reference to any previous statement.

   The trooper thanks his informant and rides slowly on, looking about him. […] He comes to a gateway in the brick wall, looks in, and sees a great perplexity of iron lying about in every stage and in a vast variety of shapes— […] "This is a place to make a man's head ache too!" says the trooper, looking about him for a counting-house.

8. 8
   adv

   to a degree exceeding normal or proper limits

Etymology

From Middle English to (“also, in addition to”), from Old English tō (“furthermore, also, besides”), adverbial use of preposition tō (“to, into”). The sense of "in addition, also" deriving from the original meaning of "apart, separately" (compare Old English prefix tō- (“apart”)). Doublet of to; see there for more.