Pass array of taxonomy terms to wp_query

The problem is ambiguity, you can’t just put in 'relation' => 'OR' in the main parameter list, because how would WP_Query know if it’s for the tax_query and not the meta_query?

For how it’s supposed to work, and where the relation parameter goes we need to refer to the official docs for WP_Query which gives us this example:

$args = array(
    'post_type' => 'post',
    'tax_query' => array(
        'relation' => 'OR',
        array(
            'taxonomy' => 'category',
            'field'    => 'slug',
            'terms'    => array( 'quotes' ),
        ),
        array(
            'taxonomy' => 'post_format',
            'field'    => 'slug',
            'terms'    => array( 'post-format-quote' ),
        ),
    ),
);
$query = new WP_Query( $args );

Setting it may be as simple as:

$myarray['relation'] = 'OR'; // untested