C:\>perl -e "system('awk \"FNR == NR { if (FNR != 1) word[$1] = $2; ne
+xt } $1 in word { print $0, word[$1] }\" DataSet2.txt DataSet1.txt')"
A 12 45 hello
A 10 12 hello
A 15 74 hello
C 11 41 blue
C 18 12 blue
B 23 15 goodbye
D 19 10 happy
D 11 12 happy
E 14 5 black
E 34 31 black

C:\>cat DataSet2.txt
id word
A hello
B goodbye
D happy
E black
C blue

C:\>cat DataSet1.txt
id x1 x2
A 12 45
A 10 12
A 15 74
C 11 41
C 18 12
B 23 15
D 19 10
D 11 12
E 14 5
E 34 31
F 10 45

C:\>
[download]

And here's the pure AWK version…

C:\>awk "FNR == NR { if (FNR > 1) word[$1] = $2; next } $1 in word { p
+rint $0, word[$1] }" DataSet2.txt DataSet1.txt
A 12 45 hello
A 10 12 hello
A 15 74 hello
C 11 41 blue
C 18 12 blue
B 23 15 goodbye
D 19 10 happy
D 11 12 happy
E 14 5 black
E 34 31 black

C:\>
[download]