Dictionary.com
definitions

thank

[thangk]
verb (used with object)
  1. to express gratitude, appreciation, or acknowledgment to: She thanked them for their hospitality.
noun
  1. Usually thanks. a grateful feeling or acknowledgment of a benefit, favor, or the like, expressed by words or otherwise: to return a borrowed book with thanks.
interjection
  1. thanks, (used as an informal expression of gratitude, appreciation, or acknowledgment).
Idioms
  1. have oneself to thank, to be personally to blame; have the responsibility: The citizens have only themselves to thank for corruption in government.
  2. no thanks to, (used to express annoyance) not owing to: I caught my flight after all, no thanks to you.
  3. thank God, (used as an interjection to express relief, thankfulness, etc.)Also thank goodness, thank heaven.
  4. thanks to, (used to express gratitude or blame) because of; owing to: Thanks to good organization and hard work, the benefit concert was a great success. The case went poorly thanks to the lawyer's incompetence.
  5. thank you, (used as an interjection to express gratitude, appreciation, or acknowledgment, as for a gift, favor, service, or courtesy).

Origin of thank

before 900; (noun) Middle English: favorable thought, goodwill, gratitude, (in singular and plural) expression of thanks; Old English thanc (in singular) expression of thanks, orig., thought, thoughtfulness; (v.) Middle English thanken, Old English thancian (cognate with Dutch, German danken); akin to think1
Related formsthank·er, nounre·thank, verb (used with object)un·thanked, adjectiveun·thank·ing, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for thank god

thank

verb (tr)
  1. to convey feelings of gratitude to
  2. to hold responsiblehe has his creditors to thank for his bankruptcy
  3. used in exclamations of reliefthank goodness; thank God
  4. I'll thank you to used ironically to intensify a command, request, etcI'll thank you to mind your own business

Word Origin for thank

Old English thancian; related to Old Frisian thankia, Old Norse thakka, Old Saxon, Old High German thancōn
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for thank god

thank

v.

Old English þancian "to give thanks," from Proto-Germanic *thankojan (cf. Old Saxon thancon, Old Norse þakka, Danish takke, Old Frisian thankia, Middle Dutch, German danken "to thank"), from *thankoz "thought, gratitude," from PIE root *tong- "to think, feel." For sense evolution, cf. related Old English noun þanc, þonc, originally "thought," but by c.1000 "good thoughts, gratitude." The whole group is from the same root as think (q.v.). In ironical use, "to blame," from 1550s. To thank (someone) for nothing is recorded from 1703. Related: Thanked; thanking.

Online Etymology Dictionary, © 2010 Douglas Harper
Idioms and Phrases with thank god

thank God

Also, thank goodness or heaven. I'm grateful, as in Thank God you arrived safely, or We didn't, thank goodness, run out of food, or Thank heaven the book arrived on time. These ejaculations originally expressed gratitude to divine providence but today tend to be used in a more casual way. [c. 1200]

thank

In addition to the idioms beginning with thank

  • thank God
  • thank one's lucky stars
  • thanks to

also see:

  • give thanks for small blessings
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.