# Read dictionary
my %abbreviations;
while (my $line = <DATA>) {
    my ($abbrev,$longname) = split/:/, $line;
    $abbreviations{$abbrev}=$longname;
}

# Process file
open my $FH, '<', 'the_file' or die;
while (my $line = <$FH>) {
    my ($field1, $field2, $key, $field3) = split /\t/, $line;
    if (exists $abbreviations{$key}) {
        # key was abbreviated, replace with full value
        $key = $abbreviations{$key};
    }
    print "$key: ($field1, $field2, $field3)\n";
}
close $FH;

__DATA__
perl:pathologically eclectic rubbish lister
lisp:lots of irritating silly parenthesis
python:all your space are belong to us
ruby:a quack language