Elegant way to examine a string by "word" (whitespace-delimited substring)

Suppose I have the following list of strings myStrList:

myStrList = {"This is A 123a Test", "This is A 123ab Test","This is A 123-a 456-B 7c-89 Test"};

I wish to create a function that takes a single string str and returns the string "words" that contain exactly one letter character.

I will define a "word" as a substring delimited by whitespace but containing no whitespace of its own. I can generate a list of string "words" by simply passing the string to the function StringSplit. For example:

StringSplit["This is A 123a Test"](* {"This", "is", "A", "123a", "Test"} *)

So the words comprising the string "This is A 123a Test" are "This", "is", "A", "123a", and "Test".

Now I wish to write a function myWordFunction that returns the words containing exactly one letter character. I can do this by using StringSplit to generate the list of words, and then I select the words with exactly one letter character:

myStrList = {"This is A 123a Test", "This is A 123ab Test", "This is A 123-a 456-B 7c-89 Test"};myWordFunction[str_String] := Module[{wordsList, substringsList},   wordsList = StringSplit[str];   substringsList =     Select[wordsList, StringCount[#, _? LetterQ] == 1 &];   Return[substringsList];   ];myWordFunction[#] & /@ myStrList

This works, but it seems rather inelegant to first split the string into words and then do the (substring) analysis and selection. Is there a way to specify a "word" (whitespace-delimited substring) directly in a (string) pattern?