In learning the meaning of words small dictionaries are very often a greater liability than they are a help.
The meanings they give are often circular: Like "Cat: An Animal. " "Animal: A Cat. " They do not give enough meaning to escape the circle.
The meanings given are often inadequate to get a real concept of the word.
The words are too few and even common words are often missing.
Huge dictionaries can also be confusing as the words they use to define are often too big or too rare and make one chase through 20 new words to get the meaning of the original.
The best dictionaries are the very large child's dictionaries like The World Book Dictionary (A Thorndike-Barnhart Dictionary published exclusively for Field Enterprises Educational Corporation, Merchandise Mart Plaza, Chicago, Illinois 60654 or Doubleday and Company. Thorndike-Barnhart has a whole series of dictionaries of which this is a special one. Field Enterprises has offices in Chicago, London, Rome, Sydney, Toronto. The World Book Dictionary is in two volumes, each 28 ½ cm [11 ¼ inches] by 22 cm [8 5/8 inches] by 5.8 cm [2 ¼ inches], so it is no small dictionary!) (Also it defines Dianetics correctly and isn't determined on a course of propaganda to re-educate the public unlike Merriam Webster's dictionaries.)
Little pocket book dictionaries may have their uses for traveling and reading newspapers, but they do get people in trouble. I have seen people find a word in them and then look around in total confusion. For the dinky dictionary did not give the full meaning or the second meaning they really needed.
So the dinky dictionary may fit in your pocket but not in your mind.